Magnetic contact structure



May E9, E942,

E. LAKATOS ETAL MAGNETIC CONTACT STRUCTURE Filed bec. 9, 1939 /NVENTORSE AKATOS A TTORNEV Fatented May i9? MAGNETEC CQN'EACT STRUCE Emory tratos, NewYork, N. Y., and Howard T.

Reeve,

Millhnm, NIJ., assignors to Bell Telephone laboratories, Incorporated, New York, N. Y., a corporation of New York 9 Claims.

This invention relates to magnetic materials for use in connection with the magnetic circuits of relays.

An object of the invention is to provide a magnetic material which While retaining its magnetic properties also has good electrical conductivity.

It has been proposed to constructl a relay, the work circuit of which is established upon the attraction of the armature to the pole-pieces of the relay core by the conductive engagement of the armature with the core, thus eliminating the contact springs usually operated by the armature and thereby simplifying the relay structure and reducing its cost. A relay of this type is disclosed, for example, in the copending application of C. N. Hickman and E. Lakatos, Serial No. 308,497, filed December 9, 1935i, in which the contact resistance between the amature and the relay core upon the engagement of the armature with the pole-pieces of the core is reduced by plating the faces of the pole-pieces or by plating both the pole-piece faces and the contact surface of the armature with a metal having good conductivity such as silver.

In accordance with the present invention it is proposed to improve the conductivity of the core pole faces and the Contact surface of the armature of a relay of this general type by welding strips thereto fabricated from a mixture of nely divided particles of iron or other magnetic material and a metal having good electrical conductivity, or by fabricating such strips with a1- ternate laminations of iron or other magnetic material and a metal having good electrical conductivity.

As illustrative o the application of magnetic .materials of the types contemplatedby the present invention, reference may be had to the accompanying drawing in which:

Fig. 1 discloses a partial top-'plan View of a relayl of the type in which the magnetic circuit elements are fabricated from the proposed magnetic material;

Fig. 2 discloses a s ide elevation View of the relay disclosed in Fig. 1; and

Fig. 3 shows a cross-sectional View of an armature and core lamination which have acings welded thereto composed of alternate laminations of iron or other magnetic material and another metal.

The relay comprises an assembly of a piurality of magnetic circuit units each comprising a. core lamination i, an armature supporting spring lamination 2 and an interposed lamination 3 of The several units are assembled side by side and insulated from eachother by spacing laminations 4 of insulating material such as hard rubber or iibre. between end blocks of hard rubber, one oi which is shown at 5, and end plates, one of which is shown at t, on threaded studs 1, 8 and 9 which extend through aligned holes in the end plates, the end blocks, the spacing laminations and the laminations comprising the units. The assembled structure is clamped together by nuts l@ threaded upon the ends of the studs. For insu.- lating the core laminations I and the spring laminations 2 from the studsI which pass through the holes therein, the studs are surrounded by sleeves I l of insulating material such as hard Each core lamination i is stamped from a sheetl of magnetic material into the Tvshaped disclosed in Fig. 2 and comprises a horizontal portion i2 having three pole-pieces I3, l@ and l5 on its upper edge formed by the two parallel slanting slots it and Il and a rear portion I8 provided with a rearwardly extending terminal lug I9.

Each spring lamination 2 is stamped from a sheet of nickel-silver and is also of the same general conguration as the core lamination having slots in its outer end for alignment with the slots i@ and Il of the associated core lamination and having rearwardly extending terminal lugs 2Q and 2i. Each spring lamination is bent at right angles along its upper edge and the bentover portion is severed from'the body of the lamination along the majory portion of its length to form a spring finger 22 which extends forwardly at a rising angle over the top edge of the associated core lamination I. An armature 23 is welded or otherwise secured to the free end of the spring finger 22 in a position to overlie the c@ pole faces of the pole-pieces I3, It and vI5 of the associated core lamination.

The insulating laminations S and also have' the same general conlguration as the core lamination and are provided with slots in their outer ends for alient with the slots I6 and ll of the core laminations. y

Normally the Working air-gaps between the pole-pieces of the core laminations and the lower faces of the armatures are maintained by a common back-stop bar 2t, the ends of which are seated in notches in the ends of the end plates, such as E, and maintained in such notches by spring members 25 secured to the ends of the back-stop bar.

A common energizing 'coil 26 is seated in the aligned slots of the core, spring and insulating laminations, thereby surrounding all of the middle pole-pieces I4 of the core laminations. The end blocks are cut away to give clearance for the ends of the coil and the block 5 is provided with two brass tubes 28 and 2t extending therethrough to the forward ends of which the tercore lamination through the attracted armature to the spring `lamination which supports the armature.

In accordance with one embodiment of the present invention, the contact resistance between the armatures and the pole-pieces of the associated core laminations may be reduced by Welding small pieces Ell of a magnetic material which is composed of a mixture of finely divided particles of iron and nely divided particles of lanother metal which has good electrical conductivity, such as silver, to the faces of the polepieces of the core laminations and to the undersurface of the armatures.

In carrying out this process of manufacture, the finely divided particles of silver maybe produced by chemical precipitation and the iron particles may be produced either by treating iron with an acid to precipitate an iron oxide and then reducing the iron oxide by hydrogen to form fine particles of chemically pure iron or, electrolytic iron may be obtained in any well-known manner, broken into small pieces and reduced to ne particles by grinding in a ball mill.4 The iron particles are then heated in anyv suitable furnace to anneal them and to drive oi .any occluded gasesprincipally hydrogen.

The silver particles and the iron particles are then mixed preferably in the proportion of 50 per cent silver and 50 per cent iron by weight, placed in a4 mold and subjected to a high vpressure, for example, of 200,000 pounds per square inch and to a temperature of 900 to 950 centigrade to form bars in much the same manner as dust cores for loading coils are molded. The bars are then rolled into sheets of the thickness required for the facing strips 30` of the armatures and core laminations and the facings are then stamped therefrom in the required shapes. If desired the strips 30 of the armatures and core laminations may be molded directly from the mixture of metal particles.

Although good results may be obtained by com bining equal Weights of silver and iron particles, the silver content may be increased and the iron content decreased proportionately to secure a material having greater conductivity However,

the iron content must not be reduced to such an extent as to render the material ineicient magnetically.

As an alternative method of combining portions of iron and portions of another metal having good conductivity, to form a magnetic material from which facing strips of the core laminations and armatures may be fabricated, thin sheets of iron may rst be electroplated with a thin coating of copper and then such electroplated sheets may be stacked together with interposed sheets aeeaeee v of a conducting metal such, for example, as sheets of silver. The stack of sheets may then be subjected to heat and pressure until a bond is established between the surfaces of the interposed sheets and the copper coatings of the iron sheets. The temperature employed if silver were used should not be greater than '778 centigrade. After the bonding has been completed, the stack is then rolled into a sheet of the thickness required and the facing strips for the armatures and core laminations are then stamped therefrom in the required shapes.

Fig. 3 illustrates in cross-section an armature and a core lamination having facing strips 30 welded thereto which are fabricated from a laminated sheet of the character just described having three laminations 3l of iron and two interposed laminations 32 of'silver or another metal having good conductivity. The facing4 strip is welded with its laminations extending laterally of the armature 23 and the facing strip is welded with its laminations extending longitudinally of the core lamination I whereby the laminations of the strips cross at right angles toeach other and when the armature 23 is attracted into engagement with the pole faces of the core lamination l, the edges of the iron laminations 3i of .both the core and armature engage to establish low reluctance magnetic paths and the edges of the silver laminations 32 of both the core and armature engage to establish low resistance cond uctive paths.

While as illustrated the thicknesses of the` silver and iron laminations have been soselected as to substantially equalize the weights of the silver and iron content, the thickness of the silver laminations could be increased and the thickness of the iron laminations proportionately decreased to further reducethe contact resistance between the armature and the core lamination. However, the iron content should not be reduced to such an extent as to materially reduce the magnetic eiliciency. Furthermore it is to be understood that the number of laminations of iron and silver in the composite structure is not necessarily limited to the number illustrated but may be varied as desired to secure the maximum magnetic and conductive eiciency.

It is to be understood that while the application of the invention has been illustrated in connection with a specific relay structure, the invention is equally applicable to any relay in which a work circuit is established by the conductive engagement of the armature with the relay core.

What is claimed is: l

1. An electrical contact element fabricated from a magnetic material having good electrical conductivity composed of a mixture of finely divided particles of iron and finely divided particles of silver.

2. An electrical contact element fabricated from magnetic material having good electrical conductivity composed of a mixture of ilnely divided particles of iron and iinely 'divided particles of silver in substantially equal proportions by weight.

3. An electrical contact element fabricatedv cesante 5. An electrical Contact element abricated from a magnetic material-composed of interposed laminatlons of iron and a metal having good electrical conductivity. A

6. An electrical contact element fabricated from a magnetic material having good electrical conductivity composed of interposed iaminetions of iron and silver.

7. An electrical contact element fooriceted from e. magnetic material composed ci laminetions of iron having coatings of copper electroplated thereon and interposed sheets of silver bonded to said laminations. 8. An electrical contact element fabricated from e. magnetic material composed of interspersed portions of a magnetic material and a metal having good electrical conductivity.

9. An electrical contact element fabricated from a magnetic material having good electrical conductivity composed of interspersed portions of e megnetic materiel and silver.

EMORY TOS. HOW T. Rm. 

